Sheet metal heat exchange stack or fire tube for gas fired hot air furnaces



March 22, 1966 REZNOR 3,241,609

SHEET METAL H n E HANGE STACK 0R FIRE TUBE FoR GAS FIRED HOT AIR FURNACES Filed March 5, 1964 2 Sheets$heet 1 III'A F l G 7 INVENTOR- GEORGE W- REZNOR m? Zia ATTO RNEY March 22, 1966 G. w. REZNOR 3,241,609 SHEET METAL HEAT EXCHANGE STACK QR FIRE TUBE FOR GAS FIRED HOT AIR FURNACES Filed March 5, 1964 2 Sheets-Sheet 2 INVENTOR.

GEORGE W. REZ NOR ATTORNEY United States Patent Ofiice 3,241,609 Patented Mar. 22, 1966 3,241,609 SHEET METAL HEAT EXCHANGE STACK R FIRE TUBE FUR GAS FIRED HOT AIR FURNACES George W. Reznor, Mercer, Pa., assignor to International Telephone and Telegraph Corporation, a corporation of Maryland Filed Mar. 3, 1964, Ser. No. 348390 Claims. (Cl. 165177) The present invention relates to gas fired hot air furnaces and has particular reference to a novel sheet metal heat exchange stack or fire tube for such furnaces. More specifically, the invention is concerned with that type of hot air furnace wherein individual flame jets emanating from a series of gas burners are directed upwardly through a series of cooperating stacks or fire tubes, while at the same time air is forced laterally across and between the tubes to extract heat therefrom, after which the thus heated air is discharged into an inhabitable or other enclosure within which the furnace is disposed, or conducted to an enclosure remote from the furnace. Still more specifically, the heat exchange fire tube of the present invention is of the two-part seam welded sheet metal type wherein, when the two sections of the tube are assembled upon each other they establish a relatively large generally fiat rectangular fire tube adapted to be set on end with the axis of the tube extending vertically. The side walls of the tube are spaced apart a slight distance and they define therebetween a combustion chamber for the upward flow of hot combustion gases, the chamber being generally of venturi shape in vertical cross section, the medial region of the chamher being of restricted width and the extreme upper and lower regions of the chamber being abruptly enlarged to establish upper and lower transversely elongated header sections within the vertical confines of the tube. The upper part of the passageway thus created for the combustion gases constricts the flow thereof to give good velocity thereto and thereby avoid a skin effect preventing good heat exchange. When installed in a hot air furnace casing, the lower header section communicates with an elongated flame producing burner therebeneath, While the upper header section communicates with a discharge header or duct for the spent products of combustion.

Sectional fire tubes of this general type and currently in use are possessed of certain limitations, principal among which is the tendency for the side walls of the fire tube to buckle under the influence of high heat conditions. If the buckling is in an inward direction the partial collapse of the tube greatly restricts the free upward flow of combustion gases through the tube. If the buckling is in an outward direction, the upward flow of gases through the tube is enhanced to such an extent that large portions of the gases are short circuited through the central regions of the combustion chamber and do not make intimate heat exchange with the side walls of the tube. Such buckling and other effects of thermal expansion of the sheet metal of the tube frequently causes creeping of the sections'on each other and increases the danger of seam opening.

The present invention is designed to overcome the above-noted limitations that are attendant upon the construction and use of conventional heat exchange fire tubes of the seam welded sheet metal sectional type and, toward this end, the invention contemplates the provision of such a fire tube wherein novel means are provided for positively preventing appreciable inward bulging of the fire tube side walls, as well as additional means for inhibiting relative vertical or lateral creeping of the fire tube side walls with respect to each other, or any combination of such vertical and lateral creeping of the side walls.

The provision of a sheet metal sectional heat exchange fire tube of the character briefly outlined above being the principal object of the invention, it is a. further object to provide such a heat exchange fire tube which, by rea son of such bulging and creeping inhibiting means, is rigidified in an over-all manner so that it is appreciably stronger and more rugged and durable than conventional fire tubes.

Numerous other objects and advantages of the invention, not at this time enumerated, will readily suggest themselves as the following description ensues.

In the accompanying two sheets of drawings forming a part of this specification, one illustrative embodiment of the invention has been illustrated.

In these drawings:

FIG. 1 is a perspective view of a sectional sheet metal heat exchange stack or fire tube constructed according to the present invention;

H1816. 2 is a side elevational view of the fire tube of FIG. 3 is a front elevational view of the fire tube of FIG. 1;

FIG. 4 is a plan view of the fire tube of FIG. 1 looking in the direction of the arrows 44;

FIG. 5 is a bottom view of the fire tube of FIG. 1, looking in the direction of the arrows 5-5;

FIG. 6 is a sectional view taken substantially along the line 66 of FIG. 2 looking in the direction of the arrows; and

FIG. 7 is a sectional view taken substantially along the line 77 of FIG. 2 looking in the direction of the arrows.

Referring now to the drawings in detail, and in particular to FIG. 1, a stack or fire tube constructed according to the principles of the present invention has been designated in its entirety at 10 and is comprised of two counterpart sheet metal stampings 12 and 14 of generally similar configuration and disposed in facing relationship along vertical marginal seam areas 16 to provide a generally tubular structure of flat rectangular design when viewed from either side thereof and as shown in FIG. 2.

As shown in FIGS. 4 and 5, the assembled composite fire tube is provided with closely spaced opposed uninterrupted side walls 18 and 20, and remotely spaced divided front and rear walls 22 and 24. The four walls 18, 20, 22 and 24 define therebetween an internal open ended passageway 25 which establishes a combustion chamber for products of combustion when the fire tube 10 is operatively installed within the casing of a hot air furnace.

The lower regions of the side walls 18 and 20 are flared outwardly at a relatively small slant angle as shown in FIG. 3, thus establishing an enlarged header section 26 at the lower end of the fire tube. The upper regions of the side walls 18 and 20 are flared outwardly and abruptly at a relatively large slant angle, thus establishing an enlarged header section 28 at the upper end of the fire tube. The intermediate portions of the side walls 18 and 20 converge upwardly at extremely small slant angles, thus lending a generally venturi shape to the first tube when considered in vertical. cross section.

The seam areas 16 are enhanced in size :by the provision of lateral attachment flanges 30 and 32 on the divided sections of the front and rear walls 22 and 24, these flanges being welded together in face to face contact. The flanges 30 and 32 are preferably full height flanges.

The side walls 18 and 20 are each provided with a plurality of vertical corrugations therein presenting alternate crest and trough portions 40 and 42 respectively.

The various crest portions are tapered downwardly and inwardly, which is to say that they are wide at their upper regions and narrow at their lower regions. The various trough portions have reverse tapers, which is to say that they are wide at their lower regions and narrow at their upper regions. As shown in FIGS. 4 and 5, the crest portions 40 of each sheet metal stamping, 12 or 14 as the case may be, are aligned with the trough portions 42 of the other stamping so that the passageway 25 within the fire tube is generally of wavy configuration in a front-to-rear direction, the corrugated walls 18 and 20 being in relatively close coextensive proximity to each other, especially in the upper regions of the tube and as best seen in FIG. 2.

The arrangement of parts thus far described is purely conventional and no claim is made herein to any novelty associated with the same, the invention residing rather in the novel means for preventing inward bulging of the fire tube side walls 18 and 20 or relative creeping thereof when changes, especially sudden changes, in combustion chamber temperatures are encountered. It is deemed pertinent to point out at this time that the heat exchange fire tubes such as have been thus far described herein are adapted for positioning, along with like tubes, in the heat exchange section of a hot air furnace and above a series of burners which supply heat to the tubes by directing an elongated flame jet into the lower header sections 26 of the various fire tubes. The upper :header sections 28 communicate with an exhaust duct which may discharge the products of combustion either interiorly or exteriorly of the enclosure within which the furnace is disposed. A blower serves to force air in a fore and aft direction between adjacent fire tubes and is discharged from the furnace casing at the front end thereof. The corrugated side walls enhance the sweeping action of both the internal products of combustion and the external air passing the fire tubes.

In order to prevent appreciable inward bulging of the fire tube side walls 18 and 20 and possible collapse of the fire tube, the crest portion 40 of one of the corrugations 40 in the side wall 20, is deformed by the provision of a transversely extending indentation 50 therein (FIG. 2). The depth of the indentation 50 is not so great that it makes contact with the opposed trough portion of the side wall 18 but is sufiiciently deep as to make such contact after a predetermined minimum degree of bulging has taken place. This minimum tolerable degree of inward bulging is however of insufficient magnitude as to permit any interlacing, however slight, of the the trough portions 62 of one fire tube section with the crest portions 40 of the other section. A similar indentation 52 (FIG. 1) is formed in the side wall 18 and serves the same purpose as the indentation 50. The two indentations appear in FIGS. 4 and where it may be observed that these two indentations 50 and 52 are widely displaced from each other in the fore and aft direction of the fire tube 10. It has been found that a single indentation in each side wall, appropriately selected as to its position and disposed well within the rectangular confines of the fire tube, will suffice to maintain both side walls against appreciable inward bulging or collapse.

In order to prevent relative creeping between the side walls 18 and of the fire tube 10, a pair of opposed transversely registering indentations 60 and 62 of relatively small magnitude are provided in the extreme upper regions of the two side walls 18 and 20, preferably medially on the sloping sides of opposed crest and trough portions of adjacent corrugations. These indentations are spot welded together as indicated at 64 in FIG. 7. In addition to preventing planar shifting of the sections 12 and 14 relative to each other, the indentations also, to a limited degree, reinforce the side walls 18 and 20 against bulging.

From the above description it will be appreciated that 4- the various indentations 50, 52, 60 and 62 not only serve to prevent bulging and creeping of the fire tube side walls, but also they serve to rigidity the entire fire tube structure. These indentations are relatively small and therefore offer little impedance to the free flow of gases vertically upwardly through the fire tube.

The invention is not to be limited to the exact arrangement of parts shown in the accompanying drawings or described in this specification as various changes in the details of construction may be resorted to without departing from the spirit of the invention. Therefore, only insofar as the invention has particularly been pointed out in the accompanying claims is the same to be limited.

I claim:

1. A generally flat and rectangular heat exchange fire tube of the character described and adapted to be positioned vertically above a combustion chamber for passage of the products of combustion issuing from Said chamber upwardly through the fire tube, said fire tube comprising two similar counterpart sheet metal sections welded together along margin-a1 sea-m lines to provide a hollow tubular structure which is open at its top and bottom and having opposed closely spaced side walls of broad rectangular expanse, and widely spaced narrow vertically extending front and rear walls, said walls defining an internal passage for combustion gases, at least one of said side walls being formed with an inwardly projecting offset protuberance in the medial regions thereof extending partially across said internal passage and terminating in close proximity to the other side wall, said protuberance and the directly opposed region of said other side wall being designed for engagement with each other when either side wall exceeds a predetermined degree of inward bulging tolerance.

2. A generally fiat and rectangular heat exchange fire tube of the character described and adapted to be positioned vertically above a combustion chamber for passage of the products of combustion issuing from said chamber upwardly through the fire tube, said fire tube comprising two similar counterpart sheet metal sections Welded together along marginal seam lines to provide a hollow tubular structure which is open at its top and bottom and having opposed closely spaced side walls and broad rectangular expanse, and widely spaced narrow vertically extending front and rear walls, said walls defining an internal passage for combustion gases, said side walls sloping generally inwardly and upwardly toward each other so that said internal passage is of relatively small width in the upper regions thereof and of relatively great width in the lower regions thereof, one inwardly projecting offset protuberance individually integral to each of said side Walls in the upper medial regions thereof extending partially across said passage in the narrow region thereof and terminating in close proximity to the other side wall, said protuberance and the directly opposed region of said other side wall being designed for engage-- ment with each other when either side Wall exceeds a predetermined degree of inward bulging tolerance.

3. A generally flat and rectangular heat exchange firetube of the character described and adapted to be positioned vertically above a combustion chamber for passage of the products of combustion issuing from said chamber upwardly through the fire tube, said fire tube comprising two similar counterpart sheet metal sections welded together along marginal seam lines to provide a hollow tubular structure which is open at its top and bottom and having opposed closely spaced side walls of broad rectangular expanse, and widely spaced narrow vertically extending front and rear walls, said walls defining an internal passage for combustion gases, each of said side walls being formed with vertical corrugations therein presenting alternate crest and trough portions, the corrugations of the two side walls being staggered so that the crest portions of each corrugation in each side wall transversely opposes a trough portion of a corrugation in the other side wall, one of the corrugations of each of said side walls being formed with 12111 inwardly ofiset pnotuberance which extends partially across said internal passage and terminates in close proximity to a corrugation of the other side Wall, said protuberance and only the directly opposite region of the opposed side wall being designed for engagement with each other when either side Wall exceeds a predetermined degree of inward bulging tolerance.

4. A generally flat and rectangular heat exchange fire tube as set forth in claim 3, wherein said protuberance is provided on the crest portion of its associated corrugation.

5. A generally flat and rectangular heat exchange fire tube of the character described and adapted to be positioned vertically above a combustion chamber for passage of the products of combustion issuing from said chamber upwardly through the fire tube, said fire tube comprising two similar counterpart sheet metal sections welded together along marginal seam lines to provide a hollow tubular structure which is open at its top and bottom and having opposed closely spaced side walls of broad rectangular expanse, and widely spaced narrow vertically extending front and rear walls, said walls defining an internal passage for combustion gases, each of said side walls being formed with vertical corrugations therein presenting alternate crest and trough portions, the corrugations of the two side walls being staggered so that the crest portions of each corrugation in each side wall transversely opposes a trough portion of a corrugation in the other side wall, one of the corrugations of each side wall being formed with an inwardly offset protuberance which extends partially across said internal passage and terminates in close proximity to a corrugation of the other side wall, said protuberance and the directly opposed region of the opposite side wall being designed for engagement with each other when either side wall exceeds a predetermined degree of inward bulging tolerance, one pair of transversely opposed corrugations on the two side Walls being formed with mating inwardly extending pro tuberances which are welded together at their apices to prevent planar creeping of the side walls with respect to each other.

References Cited by the Examiner UNITED STATES PATENTS 1,428,901 9/1922 Payne 148 2,613,920 10/1952 Flint 165148 2,866,449 12/1958 Baeza 126-91 3,058,457 10/1962 Fiedler 126-91 3,073,296 1/1963 Hol-lingsworth et al. 126-1l0 FREDERICK KETTERER, Primary Examiner. 

1. A GENERALLY FLAT AND RECTANGULAR HEAT EXCHANGE FIRE TUBE OF THE CHARACTER DESCRIBED AND ADAPTED TO BE POSITIONED VERTICALLY ABOVE A COMBUSTION CHAMBER FOR PASSAGE OF THE PRODUCTS OF COMBUSTION ISSUING FROM SAID CHAMBER UPWARDLY THROUGH THE FIRE TUBE, SAID FIRE TUBE COMPRISING TWO SIMILAR COUNTERPART SHEET METAL SECTIONS WELDED TOGETHER ALONG MARGINAL SEAM LINE TO PROVIDE A HOLLOW TUBULAR STRUCTURE WHICH IS OPEN AT ITS TOP AND BOTTOM AND HAVING OPPOSED CLOSELY SPACED SIDE WALLS OF BOARD RECTANGULAR EXPANSE, AND WIDELY SPACED NARROW VERTICALLY EXTENDING FRONT AND REAR WALLS, SAID WALLS DEFINING AN INTERNAL PASSAGE FOR COMBUSTION GASES, AT LEAST ONE OF SAID SIDE WALLS BEING FORMED WITH AN INWARDLY PROJECTING OFFSET PROTUBERANCE IN THE MEDIAL REGIONS THEREOF EXTENDING PARTIALLY ACROSS SAID INTERNAL PASSAGE AND TERMINATING IN CLOSE PROXIMITY OF THE OTHER SIDE WALL, SAID PROTUBERANCE AND THE DIRECTLY OPPOSED REGION OF SAID OTHER SIDE WALL BEING DESIGNED FOR ENGAGEMENT WITH EACH OTHER WHEN EITHER SIDE WALL EXCEEDS A PREDETERMINED DEGREE OF INWARD BULGING TOLERANCE. 